I have some difficulty with Richard Brown’s zoombie and shombie cases, as discussed by him here.
A zoombie is a creature that is identical to an actual human in every non-physical respect and which lacks non-physical phenomenal consciousness.
A shombie is a creature that is physically identical to an actual human, which has phenomenal consciousness, and which lacks all non-physical properties.
Conceivability in the sense that might support claims to a priori knowledge of possibility lies somewhere between imagining and describing. The case of a chiliagon demonstrates that our ability to conceive passes beyond our ability to ‘picture’ in our imagination. The case of the description, ‘Circular square’ demonstrates that our ability to conceive is surpassed by our ability to describe.
It seems to me that Brown’s version of conceivability is nothing but the capacity to describe and his cases are not truly conceivable.
In both the zoombie and shombie cases, we are asked to conceive of cases in which non-physical properties and phenomenal properties come apart. In the first case, we are asked to conceive of non-physical properties without phenomenal properties. In the second case, we are asked to conceive of phenomenal properties without non-physical properties.
The problem I have is that I do not know what it is of which Richard Brown is asking me to conceive. What are these non-physical properties? I know what physical properties are, well enough, by their role in our best physical theories. I know what phenomenal properties are, well enough, as they are manifest to consciousness. I do not know what properties I am supposed to otherwise be conceiving of as non-physical.
I have doubts as to whether conceivability can ground a priori knowledge of possibility. However, it seems to me that, if it does then the zoombie and shombie cases are not an example of it – or even a good example of the same reasoning used by Chalmers, by way of reductio. This is because I take it as a necessary, but not sufficient, condition for conceivability that one can conceive of distinct instances of the same property or the same relevant kind of state of affairs. In the case of the chiliagon, I can conceive of a red one, a blue one, a large one, a small one. I can vary the cases while clearly apprehending a property of chiliagon-ness which remains invariant in each instance.
In talking about non-physical properties apart from phenomenal properties, there does not seem to be any but one way (allowing for paraphrasing) to describe what we are being asked to conceive of. This suggests to me that it is an obvious case of a mere description and nothing of which we may conceive.
To be clear, I am not saying that we can’t conceive of many cases in which things have only physical properties. Of course, we can conceive of entirely physical worlds which, by definition, have physical properties and no others. It seems to me that Brown is asking us to do more than this. He is asking us to positively conceive of non-physical properties and for us to do so without giving us any understanding of them that would allow us to differentiate instances conceived of. In the case of zoombies, Brown is asking us to conceive of something possessing properties of the kind Non-P without providing any guide as to what Non-P is. Granted, in the case of shombies, Brown is asking us to conceive of something that does not possess properties of the kind Non-P. However, there is still a difference between saying that properties of kind P exhaust the properties of a world and saying that the same world does not instantiate properties of kind Non-P. If we claim that a world does not instantiate Non-P then we still have to be able to conceive of Non-P, whereas the former claim that properties of the kind P are all there is merely relies on conceiving of properties of which we can conceive of their multiple instantiations.
Now, it might be thought to respond to this by coming up with some alien, non-physical property, e.g. ectoplasmic non-resistance, and thus provide a non-physical property to conceive of in the zoombie and shombie cases. However, this will not do at all because the dualist never claimed that these trumped-up non-physical properties, in particular, had any relation to phenomenal consciousness. We can all agree that there can be ectoplasmic non-resistance without phenomenal consciousness and phenomenal consiousness without ectoplasmic non-resistance.
Also, I might be wrong about the shombie case and Brown might say that he means that he can conceive of a world that only has physical properties and yet still has phenomenal consciousness. I suppose someone could also claim that they can conceive of a circular square in a flat, Euclidean space. Further, the claim that an entirely physical world could still have phenomenal consciousness is shown by the original zombie argument to be relevantly like the claim that circular squares are conceivable. Remember, Chalmers requires that possible cases are IDEALLY conceivable, which means that some claims of conceivability can be dismissed as irrational.
In conclusion, zoombie and shombie cases are not conceivable and do not hurt Chalmers’ formulation of the zombie argument.
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